The present invention generally relates to injection blow molding machines, and in particular to clamping devices that are used to apply a clamping force to mold parts used in injection blow molding machines.
A typical thermoplastic injection blow molding machine uses a clamping device to apply a clamping force that holds the parts of a mold together while either a hot thermoplastic resin is injected into a clamped injection mold to form a preform (parison), or a gas (typically air) is injected into a preform to form a blow-molded product, such as a bottle or other container, that takes on the shape of the interior of the clamped blow mold. A mold generally comprises a two-part machined article. Adjoining faces of the mold parts, or halves, are brought together and clamped for forming the preform or product, and separated for releasing the preform or product from the mold. For the typical three-station injection blow molding machine, a core rod is used to transfer the preform from the injection station to the blow mold station, and to transfer the product from the blow mold station to the product removal station where the product is stripped from the core rod.
There are generally two types of clamping devices. The first is referred to as a C-frame design that has a series of hydraulic clamping cylinders mounted directly to the C-frame assembly. Clamping cylinders are mounted over the mold parts and push downward against the top of the mold parts to apply clamping force. A benefit of the C-frame design is the absence of any frame components or tie bars in the molding area (i.e., the volume between the mold parts when the clamping device is in the opened position) that could limit access to the molding area. The mold parts are clamped between the overhead cylinders and a machine table that forms a fixed platen for the lower mold half. Therefore the frame of the machine must resist the clamping forces exerted by the hydraulic clamping cylinders. However, in this arrangement, the cylinders are more readily accessed for maintenance and replacement.
The second type of clamping device is referred to as a tie-bar design that incorporates a pair of tie-bars and bushings connecting an upper and lower yoke assembly. The machine table is situated directly between the two yoke assemblies. Hydraulic cylinders are mounted under the machine table between the table and the lower yoke assembly. As the actuators on the hydraulic cylinders extend, the upper yoke assembly is pulled downward toward the table, and the mold parts are clamped between the machine table and upper yoke assembly. For this design, the structural frame of the machine does not have to resist the clamping forces. However, as the blow-molded product increases in diameter, the height of the joined blow mold halves increases. Consequently, the length of tie bars and mold strokes require that the table height be increased, since the lower yokes must move the same distance as the upper yokes. The height requirement of the table can become so great that a raised structural platform must be provided for an operator to operate the machine. Hydraulic cylinders are located beneath the table. Further maintenance or replacement of the hydraulic cylinders is difficult due to the location of the cylinders.
Therefore, there is the need for an improved clamping device that will provide unrestricted access to the molding area of the machine and allow better arrangement of machine components.
In one aspect, the present invention is an apparatus for and method of clamping a multi-part mold used in an injection blow molding machine and process wherein two or more locking columns are commonly mounted with a first mold part, and two or more locking collars are commonly mounted with a second opposing mold part. To clamp the mold parts, the first mold part, and two or more locking columns, are moved towards the second opposing mold part and two or more locking collars so that the opposing facing surfaces of the mold parts meet, and the columns lock into the collars. After locking, clamping force is applied to the mold parts by the interlocked column and collar elements. Columns and collars may be arranged to provide a maximum clearance distance between the mold parts in the opened position. The means for bringing the first and second mold parts together and separating them is separate from the clamping means.
In another aspect, the present invention is an apparatus for and method of injection blow molding wherein at least the injection mold parts or the blow mold parts are clamped together by joining two or more locking columns, commonly mounted with a first mold part, with two or more locking collars, commonly mounted with a second mold part. After joining opposing surfaces of the first and second mold parts and locking opposing two or more locking columns and collars, clamping force is applied to the mold parts by the interlocked column and collar elements. The means for bringing the first and second mold parts together and separating them is separate from the clamping means.
In another aspect, the present invention is an apparatus for and method of injection blow molding wherein the injection mold parts and the blow mold parts are clamped together by joining at least three locking columns, commonly mounted with a first injection and blow mold parts to an A-shaped upper yoke, with at least three locking collars, commonly mounted with a second injection and blow mold parts to a fixed platen. After joining opposing surfaces of the first and second injection and blow mold parts and locking opposing two or more locking columns and collars, clamping force is applied to the injection and blow mold parts by the interlocked column and collar elements. The means for bringing the first and second injection and blow mold parts together and separating them is separate from the clamping means.
Other aspects of the invention are set forth in this specification and the appended claims.